overlayfs: Kernel panic - not syncing: Attempted to kill init! exitcode=0x00000100

Reproduce the panic using the supplied initramfs-tools files at /usr/share/initramfs-tools/hooks/ro_root and /usr/share/initramfs-tools/scripts/init-bottom/ro_root, then compare kernel-panic.txt with successful-boot.txt. Start with the overlayfs mount and the init-bottom script, and consider the issue done when the generated initramfs boots with a working read-only root filesystem without requiring the /dev/console write.

Setting up a root file system as read-only with the help of overlayfs, I can reliably reproduce a kernel panic. It looks very much like a kernel bug to me, although I am not perfectly sure about this.

It occurs when mounting an overlay in a shell script in an initramfs like this:

mount -t overlay -o "lowerdir=${ROOT_RO},upperdir=${UPPER},workdir=${WORK}" root.union "${rootmnt}"

and later exiting the script. If I write anything into /dev/console after the mount command and before exiting the script, it works fine.

To reproduce

1. Write the current lite release 2019-09-26-raspbian-buster-lite.img onto an SD card: sudo dd if=2019-09-26-raspbian-buster-lite.img of=/dev/mmcblk0 bs=1M
2. Boot from that SD card on a Raspberry 3B+, log in as pi, set date, apt-get update, apt-get upgrade, apt-get dist-upgrade.
3. Place the two files from initramfs-tools.zip at /usr/share/initramfs-tools/hooks/ro_root and /usr/share/initramfs-tools/scripts/init-bottom/ro_root.
4. Create an initramfs: sudo mkinitramfs -o /boot/initrd.img-4.19.75-v7+ 4.19.75-v7+.
5. Activate the initramfs by appending initramfs initrd.img-4.19.75-v7+ followkernel to /boot/config.txt.
6. Reboot.

Expected behaviour
Properly booting Raspbian with a working read-only root file system

Actual behaviour
A kernel panic

Output of the console via UART (after disabling bluetooth in config.txt with dtoverlay=pi3-disable-bt): kernel-panic.txt

When activating the last line in /usr/share/initramfs-tools/scripts/init-bottom/ro_root
echo "" > "${rootmnt}"/dev/console

and regenerating the initramfs
sudo mkinitramfs -o /boot/initrd.img-4.19.75-v7+ 4.19.75-v7+

it works fine: successful-boot.txt

Note that the particular device node /dev/console is important. Things like e.g. /dev/ttyprintk do not work for me.

System
Output of raspinfo after successful boot: raspinfo.txt